Parts formed from various metals, such as 2000- and 7000-series aluminum alloys, may be joined by friction stir welding, which has conventionally been associated with simple joint configurations, such as butt joints. Workpieces having more complicated joint geometries, such as corner joints, are friction-stir-welded either from only one side, limiting weld penetration, or from both sides in a sequential manner, which requires plural fixturing operations and additional fixturing equipment, resulting in increased cycle time and manufacturing cost.